We propose to study the physiology, biochemistry and pharmacology of compounds that are used or have been proposed for use in the radiographic opacification of the gallbladder and bile ducts in order to 1) provide basic data concerning the mechanism of absorption, uptake and excretion of these compounds that have been used empirically in large quantities for many years, 2) provide a rational basis for the selection of the best compound and for the most efficient, safe and economical use in clinical practice, 3) to use these data to elucidate the basic mechanisms involved with hepatic biochemistry and physiology, especially as they relate to bilirubin metabolism and 4) to develop an improved, safer and more efficient biliary contrast agent and 5) to use these data to develop contrast materials for use with computerized tomography for evaluation of the pancreas. The last would extend the usefulness of computerized tomography and allow diagnosis of cancer of the pancreas and other diseases at an earlier stage than ever before possible.